Sex May Modify the Effects of Macronutrient Intake on Metabolic Syndrome and Insulin Resistance in American Indians: The Strong Heart Study

Background: Diet has been related to several characteristics of metabolic syndrome (MSDR) and insulin resistance, which carry an increased risk for diabetes and heart disease. Objective: To examine the cross-sectional association between macronutrient intake, sex, and MSDR and insulin resistance in American Indians without diabetes. Design: Dietary intake, MSDR, and insulin resistance (estimated by homeostasis model assessment) were assessed. Subjects/setting: Data were analyzed from participants with complete dietary data (n=1,516 for MSDR, n=1,458 for insulin resistance) from the second examination (1993-1995) of the Strong Heart Study, a longitudinal, population-based study of cardiovascular disease and its risk factors in American Indians. Statistical analyses: Logistic regression and analysis of covariance were used to study associations among tertiles of macronutrient intake and MSDR and homeostasis model assessment scores. Results: Polyunsaturated fatty acid intake was associated with less MSDR and lower homeostasis model assessment scores in women (odds ratio 0.69 and 95% confidence interval 0.50 to 0.96 for MSDR in the third tertile) but not men. Higher simple carbohydrate intake was associated with more MSDR in men (odds ratio 1.72 and 95% confidence interval 1.10 to 2.69 in the third tertile) but not women. Conclusions: Polyunsaturated fatty acid and simple carbohydrates may be associated with MSDR and insulin resistance in American Indians and sex may modify the association between dietary intake and MS and insulin resistance in this population. Further studies should focus on the longitudinal association between dietary intake and incidence of MSDR and insulin resistance and the role of sex in this relationship in American Indians and other populations.